Long wire v-antenna system

ABSTRACT

Long wire antenna arrays comprising combinations of V antennas have wide-band directive characteristics when the antennas are inclined above ground and spaced from each other to make side lobe nulls and peaks of the pattern of each V antenna substantially coincide with peaks and nulls, respectively, of the array factor. Pairs of V antennas can be connected end-to-end with their apexes at the extreme ends to form tandem-V antennas, which can be arrayed with other tandem-V antennas. The arrayed antennas (V and tandem-V) are generally aligned laterally but offset from each other longitudinally and/or vertically. Space-saving arrays of V and tandem-V antennas have corresponding apexes coincident in the lateral and longitudinal directions and have the intermediate connections of one antenna longitudinally spaced from the corresponding interconnections of the other antenna. In other arrangements, V antennas having successively increasing apex angles are arrayed in circular sectors with all the Vantenna legs extending along radial paths from a common center.

atent [191 [451 Sept. 4, 1973 [73] Assignee: Sanders Associates, Inc., Nashua,

N.l-l.

22 Filed: May 12, 1969 211 Appl. No.2 827,088

Related u.s. Application 11m [63] Continuation of s... N0. 665,111, Sept. 1, 1967, which is a continuation-in-part of Ser. No. 354,974, March 26, 1964, abandoned.

[75] Inventor:

343/854 [51] Int. Cl. H0lq 11/06 [58] Field of Search ..343/731-740, 809, 854

[56] References Cited UNITED STATES PATENTS 1,974,387 9/1934 Carter 343/809 OTHER PUBLICATIONS Jasik, Antenna Engineering Handbook TK 7872 A6J 3 C.2, Oct. 1961, pp. 4-2, 4-12, 4-13, 4-14, 4-15, 4-26, 4-30, 4-31.

RCA TN No. 205, Laport, Jan. 5, 1959.

Antenna Engineering Handbook, Jasik TK 7872 A6J3 C.2, Oct. 9, 1961, pages 4-2, 4-14, 4-26, 4-30. Fernandes, Electrical Communications, Vol. 36, No. 1, 1959, pages 30-41.

Primary Examiner-Eli Lieberman Attorney-Louis Etlinger [5 7 ABSTRACT Long wire antenna arrays comprising combinations of V antennas have wide-band directive characteristics when the antennas are inclined above ground and spaced from each other to make side lobe nulls and peaks of the pattern of each V antenna substantially coincide with peaks and nulls, respectively, of the array factor. Pairs of V antennas can be connected end-toend with their apexes at the extreme ends to form tandem-V antennas, which can be arrayed with other tandem-V antennas. The arrayed antennas (V and tandem-V) are generally aligned laterally but offset from each other longitudinally and/or vertically. Space-saving arrays of V and tandem-V antennas have corresponding apexes coincident in the lateral and longitudinal directions and have the intermediate connections of one antenna longitudinally spaced from the corresponding interconnections of the other antenna.

In other arrangements, V antennas having successively increasing apex angles are arrayed in circular sectors with all the V-antenna legs extending along radial paths from a common center.

17 Claims, 20 Drawing Figures PAIENTEDSEP 41915 3.757. 341

SHEET 1 OF 9 lNl/ENTOR Arnold W. Gilbo AYYCRNE" PATENTEDSEP 41m SHEET 2 OF 9 Pmimmssw 3.757. 341

SHEET R (If 9 llO INVENTOR Arnold W. Gilb 'pfif A ATTORNEY PAIENIEDSEP' 3.757, 341

SHEEI 5 OF 9 FILE. 1?.

IN VEN TOR ATTORNEY PAIENTEDSEP 41911 3.757. 341

sum 5 or 9 I86 I94 I90 /NVEN7'0R Arnold W. Gilbo- ATTORNEY Pmmmsi 3.7571341 SHEEI 7 0F 9 BALUN BALUN h 232 TRANSMITTER 232 )CROSSOVERL 228 g NETWORK T 2289 228 4 RECEIVER 2289. F IG. I6

F I 7 INVENTOR.

ARNOLD W. GILBO ATT RNEY k. w w m m2 wm m0m wcEa I c... x

VERTICAL HORIZONTAL VERTICAL HORIZONTAL POLARIZ- POLARIZ- POLARIZ- POLARIZ- ATION k ATION ATION ATION V Y BEAM 3 INPUT PORTS BEAM 4 INPUT PORTS INVENTOR. ARNOLD W. GILBO Y K ATTORNEY LONG WIRE V-ANTENNA SYSTEM This is a continuation of application Ser. No. 665,1 1 I, filed Sept. 1, 1967 which in turn is a continuation-in-part of application Ser. No. 354,974, filed Mar. 26, 1964, now abandoned titled HIGH GAIN AN- TENNA SYSTEM WITH LOW SIDE LOBES and assigned to the assignee hereof.

This invention relates to long wire antennas, particularly to long wire V-type and tandem-V antennas. More specifically, it relates to systems of such antennas providing high directive gain and unusually low side lobes over a wide range of frequencies.

The invention also comprehends a novel feed system that operates certain antennas with multiple polarization sensitivity, so that horizontally and vertically polarized signals-can be received or transmitted simultaneously.

A V antenna comprises two diverging conductors generally fed at their apex. Terminating resistors are conventionally connected between the remote ends of the conductors and a common point, generally ground. The main lobe of the free space radiation pattern is directed along the center line of the V.

A tantem-V antenna comprises four conductors arranged in two oppositely disposed Vs with their apexes spaced apart along the antennas main lobe axis. The conductors extend between the apexes, with one conductor of each V connected in series with a conductor of the other V. The conductors are generally fed at one apex and terminated with a resistance at the other. When the-antenna is electrically symmetrical about the main lobe axis, as in most conventional designs, the terminating resistor is connected between the two conductor ends forming the apex remote from the feed apex. In free space, the radiation pattern of a symmetrical tandem-V antenna having its conductors in one plane has a single main lobe directed along the main lobe axis.

A rhombic antenna is a tandem-V antenna in which the conductors of the two Vs have the same length. However, the term rhombic antenna is also sometimes used in the art to refer to unequal-V tandem-V antennas.

Long wire tandem-V and V antennas are constructed with conductors that are more than a wavelength long at the frequencies of operation. The two conductors forming each V in such antennas can be regarded as forming a two-wire transmission line. The resistive termination is matched to the characteristic impedance of the line and, accordingly, absorbs substantially all energy reaching the terminated end of the antenna.

Under these circumstances, the current distribution along the conductors is somewhat similar to that in a conventional two-wire transmission line. Since the conductors generally do not correspond electrically to a half-wave length transmission line, the antennas are also referred to as nonresonant antennas.

As stated above, the radiation patterns of V and tandem-V antennas generally have relatively directional main lobes. The antennas do not require reflectors, and they can be made very large. Accordingly, they are used, for example, as ultra high power transmitting antennas and as highly sensitive receiving antennas. V and tandem-V antennas are thus particularly suited for long range communication and surveillance.

A further characteristic of long wire antennas, particularly V and tandem-V arrangements, is that they are generally operated as end-fire systems.

An antenna system has a space characteristic or radiation pattern generally including at least one main lobe containing most of the radiated power-and a plurality of side lobes oriented in various directions and separated by deep nulls. Voids in the main lobe of the radiation pattern result in gaps in the range coverage that the antenna system provides. Such voids can cause loss of contact with a station, such as an aircraft, that is supposedly positioned within the main lobe. Main lobe voids are accordingly undesirable and much effort is often expended in eliminating them from the pattern of an antenna system.

During transmission, energy radiated in side lobes detracts from the intensity of the energy in the main lobe and is generally wasted.

Also, energy radiated in side lobes often interferes with communication being carried out at other stations.

Conversely, when an antenna system is connected with a receiver, energy intercepted in the side lobes produces undesirable noise and/or interference at the receiver. Such noise decreases the ability of the receiver-antenna system to detect at low signal to noise ratios and hence diminishes the range of the system.

Moreover, when a signal intercepted in a side lobe has substantial strength, it may be confused with a signal being intercepted in the, main lobe. As a result, the existence of a source in the coverage of the main lobe, and its exact location, may be difficult to determine.

A further characteristic of antenna systems is fre quency band over which the radiation pattern maintains a specified configuration. For a conventional horizontally disposed rhombic antenna, the operating frequency range is generally given as 2:1 or less.

A general object of the present invention is to provide improved long range antenna systems.

It is also an object of the invention to provide a long wire antenna system having high directive gain. Further objects are that the main lobe of the antenna system be free of nulls or minima and that the system maintain these characteristics over a wide range of frequencies.

Another object of the invention is to provide V and tandem-V antenna systems of the above character.

It is also anobject of the invention to provide wideband (multi-octave) V and tandem-V antenna systems in which the amplitudes of the side lobes are much smaller than the amplitude of the main lobe.

A further object of the invention is to provide an antenna system characterized by the above features even though positioned near the earths surface.

\ Another object of the invention is to provide a feed system for operating long wire antennas, particularly V and tandem-V antenna systems, with two relatively independent communication modes, wherein the two modes can utilize the same modulation and frequency.

A further object of the invention is toprovide long wire, and particularly V and tandem-V, antenna systems that are sensitive simultaneously tov polarizations in two different planes and can distinguish between such polarizations. 7

Other objects of the invention will in part be obvious and will in part appear hereinafter.

DESCRIPTION OF FIGURES I The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a pictorial representation of the geometrical terms used in describing the invention;

FIG. 2 shows a side elevational view of a single tandem-V antenna;

FIG. 3 is a pictorial representation of an array of rhombic antennas embodying the invention; this Figure also illustrates features of a representative radiation pattern;

FIG. 4 is a plan view, partly in schematic form, of an array of inclined rhombic antennas incorporating the invention;

FIG. 5 is a side elevation view of the array of FIG. 4;

FIGS. 6-9 are graphs illustrating the elevation plane performance of an antenna embodying the invention;

FIG. 10 is a plan view, partly in schematic form, of another array of rhombic antennas embodying the invention;

FIG. I l is a side elevation view of the array of FIG. 10;

FIG. 12 is a pictorial representation of an array of V antennas embodying the invention;

FIG. 13 is a plan view, partly in schematic form, of a rhombic antenna having a feed system embodying features of the invention;

FIG. 14 is a plan view, partly in schematic form, of a composite array comprising two arrays of the type shown in FIG. 10;

FIG. 15 is a side elevation view of the composite array of FIG. 14;

FIG. 16 is a perspective view of a high-low tandem rhomboid array embodying the invention and showing in schematic form a feed system for operation with it;

FIG. 17 is a plan view of the tandem rhomboid array of FIG. 16;

FIG. 18 is a plan view of a parasol array embodying the invention;

FIG. 19 is a simplified vertical section of the parasol array taken along the lines 19-49 of FIG. 18; and

FIG. 20 is a schematic representation of a multiple beam, multiple polarization feed system for the parasol array.

SUMMARY OF INVENTION I have found that long wire antennas and systems of such antennas can be arranged to have remarkably directive patterns with high concentrations of power in single main lobes that are essentially free of nulls or minima. The antennas radiate a minimal amountof energy in side lobes. Moreover, their frequency ranges are generally much greater than that of prior long wire antennas. That is, the antennas embodying the invention maintain a low input VSWR and a high-gain directive pattern for frequency ranges generally extending at least over several octaves.

The spatial distribution or pattern of the energy radiated from an array of identical antennas is the product of the pattern of a single antenna and several array factors that are functions of the relative positions and the phasing of the antennas.

According to one feature of my invention, two nonresonant long wire antennasare overlapped and arranged with the main lobes of the individual antennas aligned in space to add. This results in a high-gain array main lobe. Further, the side lobe peaks and nulls of each individual antenna are arranged to coincide in space with the nulls and peaks, respectively, of the combined array factor for the two antennas.

That is, in the ideal case, the two antennas are arrayed with each side lobe'peak of the individual antenna patterns coinciding with a null of the array factor and with each side lobe null of the individual antenna patterns coinciding with a peak of the array factor. The resultant array pattern then has maximum concentration of power in the main lobe with a minimum of energy diverted to side lobes. The amplitudes of each remaining side lobe is many times less than that of the main lobe.

The ground below the two arrayed long wire antennas reflects energy incident upon it. When the reflected energy coincides in space with energy radiated directly from the array, the two components subtract in directions where they have a relative'phase difference equal to an odd number of half-wavelengths. Such directions, conventionally identified by elevation angles, are termed height-factor null positions. Nulls that develop in the primary lobe of the array due to such frequencysensitive, cancellation are effectively minimized according to the invention by inclining the main lobe axis of the arrayed antennas so that a minimal amount of energy is reflected to the position of the primary heightfactor null.

Thus the directly radiated energy in the main lobe is, at most, only slightly diminished by the minimal amount of reflected energy that subtracts from it at the first height-factor null position.

Inclining the antennas generally diminishes also the energy reflected to other height-factor null positions. Moreover, the two arrayed antennas produce relatively small side lobes so that the reflected energy from such side lobes produces relatively negligible cancellation at the other height-factor null positions.

In this manner, the arrays of the invention attain remarkably high-gain directive patterns that remain relatively uniform over an extended frequency band.

Pairs of V and tandem-V antennas are advantageously arrayed in this manner. Thus, although the invention is described principally with reference to tan dem-V antennas, it should be understood that it is applicable to other long wire antennas, such as the V configuration.

As also described more fully below, a single long wire antenna can be inclined with respect to ground, or other reflectors, to diminish nulls due to reflections, thereby improving the vertical characteristic of the antennas radiation pattern.

The antenna systems of the invention are designed to provide patterns that represent selected solutions of the equations for the radiation pattern of a generalized long wire antenna structure. These equations are presented below.

The invention also provides a novel feed circuit for a long wire antenna, such as a V antenna, having at least two conductors. The feed system is capable of independently coupling two sources to the antenna. One source causes the antenna to radiate main lobe energy polarized parallel to the plane of the antennas conductors. The feed applies the output from the other source to cause the antenna to radiate main lobe energy polarized transversely to the antennas reflector. The feed system provids the same operation during reception, intercepting radio waves polarized in both planes and diverting them to separate receivers.

The feed system is advantageously used with an antenna whose conductors lie in a horizontal plane to detect signals regardless of their polarization, or, during transmission, radiate signals that can be detected by any antenna within range. This performance is particularly suited, for example, for passive reconnaissance stations and for radio beacons.

Alternatively, the feed system enables the antenna to be connected with two sources of different signals and to radiate the signals with different polarizations that have low interaction.

DESCRIPTION OF PREFERRED EMBODIMENTS Considering the invention in greater detail, it can be shown that a wire extending above ground and energized at one end with a current I, and terminated at the other end radiates a pattern whose electric field components at a point P located a great distance r from the wire are given by and E E +E exp[jiKhcos(il] where E is the total electric field strength polarized parallel to the plane of incidence and transverse to the wire, the wire extends in the direction 0 and d),

E 0 d is the direct electric field component polarized field components polarized perpendicular to the" plane of incidence E 4, 4 and E 4, are expressed as where COSlll cos 0 cos 0 sin 0' sin 0 cos (4 and 10 L i J' o) A 41m, V (10) where V=a=jK I-cos ll! c0541 cos 0' cos 0 sin 0 sin 000s Further,

K (211-0.) where A is the wavelength, 1 is the length of the wire antenna, a is the attenuation constant, and h is the height of the wire at the point of phase refer ence, commonly the feed point.

the vector A, with its feed point at the origin of the illustrated coordinate system. a

When the wire is in free space, its radiation pattern components are as in Eqs. (1) and (2) with E0 E zero. v

The vertically polarized component of field strength of a tandem-V antenna at any point P (r,0,), can be expressed in terms of its direct wave and its ground reflected wave as:

and the direct and indirect waves have opposite polarinspace and well beyond the induction field of the antenna.

E is thus the vector sum of the direct and ground reflected waves at any point in space. It gives the magnitude and phase of the resultant wave, and its components can be expressed as The details of an antenna array 30 comprising planar tandem-V antennas l and 12 will now be discussed with reference to FIGS. 4 and 5. The antenna has conductors or legs 36 and 38 arranged in a V. The ends of the conductors 36 and 38 at the apex of the V form the feed point 40 of the antenna 10. A conductor 42, in series with the conductor 36 at its end 36a, is arranged in a V with a conductor 44 in series with the conductor 38. A terminating resistor 46 is connected between the conductors 42 and 44 at their apex.

The tandem-V antenna 12 similarly comprises conductors 48 and 50 arranged in a V and conductors 52 and 54 arranged in a second V having a terminating resistor 56 connected at its apex. The feed point 49 of the antenna 12 is at theapex formed by the conductors 48 and 50. The conductors 36, 38 and 48 and 50, forming corresponding Vs of the two antennas, are appropriately of the same length, as are the conductors 42, 44, 52 and 54.

As seen in FIG. 5, the conductors of the antennas l0 and 12 are suspended from towers 62 for elevation above ground, indicated at 64. The conductors of the illustrated antennas lie in parallel planes spaced apart a distance S measured transverse to the planes. Moreover, in accordance with the invention, the antennas 10 and 12 overlap each other in the array 30 with their main lobe axes 14 and 16 lying in the same plane. The beam axis 24 (FIG. 3) lies in the plane of the axes 14 and 16; this plane also bisects the main lobe 22, which is directed in the forward direction, i.e. from the antenna feed points toward the terminations.

The overlapping antennas l0 and 12 are spaced with respect to each other along the axes 14 and 16 by a distance S indicated in FIG. 4. The spacings S and Sy of the antennas 10 and 12 are so selected, as detailed hereinafter, that nulls of the individual radiation patterns coincide in space with peaks of the array factor of the two antennas. Similarly, with preferred spacings, the side lobe peaks of the individual radiation patterns coincide in space with nulls of the array factor. Since proaches zero in a deep null, in each direction about the array 30 where a null of the antennas l0 and 12 coincides with a peak of the array factor, and vice versa, the-resultant energy intensity is small. The array 30 thus diverts little energy to side lobes, and hence concentrates its radiated energy in the main lobe, producing a correspondingly high directive gain.

Moreover, the main lobe of the array 30 is thinner than the main lobes of its constituent tandem-V antennas. More specifically, as one moves away from the beam axis 24 (FIG. 3), the amplitude of the main lobe diminishes according to a cosine function of the direction angle with respect to the beam axis.

To radiate energy from the double tandem-V array 30, a feed system indicated generally at 58, FIGS. 4 and 5, and illustrated as a two-conductor transmission line having an input port 59, applies radio frequency voltage from a transmitter 60 across the feed point 40 and, preferably with equal amplitude, across the feed point 49. As the energy from the transmitter 60 travels along the antenna conductors toward the terminating resistors, a substantial amount radiates into space. The balance of the energy arrives at the terminating resistors 46 and 56, which are matched to the characteristic impedance of the conductors so as to reflect substantially no energy back toward the feed system 58.

The feed system 58 is constructed according to conventional techniques, with a phase delay from the port 59 to the feed point 49 of antenna 12 which is (Z'ITS /T) radians greater than the delay from the port 59 to the 5 feed point 40 of antenna 10. As a result, the main lobes of the two antennas l0 and 12 are in phase and reinforce each other.

In addition to adjusting the spacings S and S to minimize the amplitude of the side lobes in the pattern of the array 30, the conductor length, the elevation of the conductors, and the tilt angles can be adjusted to enhance the concentration of the power in the arrays main lobe. The tilt angles are the angles between each conductor 36, 42, 38 and 44 and the transverse axis 18, and between the conductors 48, 52, 50 and 54 and the transverse axis 20. The relation between leg length and tilt angle is discussed, for example, on page 881 of Electronic and Radio Engineering, F. E. Terman, 4th

Ed., McGraw-Hill, 1955. This text and the references cited therein dicuss conventional techniques for calculating the dimensions of a single rhombic antenna.

Considering againthe double tandem-V array shown in FIGS. 4and 5, the resultant field strength, F for one polarization component is I I COS where A is the elevation angle of the direction in interest and 4) is the azimuth angle of the direction in interest. Also,

The array factor F H is thus seen to be a cosine function of (S IA) times the cosine of the angle to the point of interest. The factor F is a cosine function of (S times the sine of the elevation angle.

The use of the array factors F H and F V in arraying antennas according to the invention is indicated in Table I-wherein Eqs. (50) and (52) are evaluated:

l. in the forward direction alongtlie an? (FIG. 3

i.e. (IF A O 2. in the lateral directigi along a plane trans-verse to the axis 24, Le. A 90 and (I) varies between I ence between them is equal to an odd number of half tion made possible with the present invention is equally effective on polarization components parallel to and transverse to the plane of each antenna. Thus, when, for example, the array is designed according to the invention to optimize the pattern of the laterally polarized-radiation component, it has been found that the pattern of the transversely polarized radiation component also has minimal side lobe levels and a correspondingly high-gain main lobe.

Still considering FIGS. 4 and 5, a reflector such as ground in the field of array reflects energy incident upon it. The reflected and direct waves coinciding in space subtract from each other when the phase differand 90, and 3. in the backward direction along the'axis '24, i.e. [I] j. l 559.14% 0 L TABLE I Forward direction Lateral direction Backward direction \l1=A=0 il =90 IP=A=180 Array factor Fv- Vi! cos For antennas fed in phase with each other, Table I indicates that factor F has a frequency invariant peak in the lateral direction and the factor F v has frequency invariant peaks in the forward and backward directions. However, as mentioned above, the feed system 58 (FIGS. 4 and 5) energizes the antennas with a relative phase difference such that the energy from the two antennas adds in the front direction along the axis 24 (FIG. 3).

wavelengths. The resultant pattern then has a minimum value, termed a height factor minimum. The direct and reflected waves add, producing a height factor maximum, when the phase difference is equal to an integral number of wavelengths.

The resultant pattern of an antenna system above ground accordingly varies with the elevation angle to the point of interest and also with frequency. This is demonstrated by the information in Table II, showing,

It has also been f nd that h p ing can advanfor a rhombic antenna, the elevation angles at which tageously be selected to bring together, in space, a null of the array factor F H with the antenna pattern (F,) side lobe peak closest to the axis 24 in the forward direction. As a result, the array factor null effectively cancels the antenna side lobe peak so that the pattern of the array has only a small side lobe, if any, in the direction of the former unwanted peak.

More generally, the spacing S is adjusted to minimize side lobes that would otherwise appear in the forward direction at small angles with respect to the main lobe axis 24, and to minimize side lobes in the backward direction.

With the antennas 10 and 12 fed with a selected phase difference corresponding to the spacing S the the first height factor minimum and maximum occur at different frequencies.

In order to maintain a frequency invariant main lobe, reflections from ground must not substantially interfere spacing Sy (FIG. 5) is adjusted to cancel remaining with the main lobethis reason, the antennas 10 peaks of the antenna pattern F I by means of nulls in the array factor F Judicious control of the spacing S has been found particularly suitable for cancelling singleantenna side lobe peaks in directions oriented at between 20 and 90 with respect to the forward direction on axis 24.

When the tandem-V antennas 10 and 12 are energized with a radio frequency voltage applied across the conductors 36 and 38 and across the conductors 48 and 50, the radiation from each antenna is principally polarized parallel to the plane of its conductors, referred to hereinafter as lateral polarization. However, only in the plane of each antenna in its radiation entirely free of components polarized transverse to the plane containing the conductors. The magnitude of the transversely polarized component increases in the direction away from the plane of each antenna.

The side lobe cancellation and main lobe concentraand 12 are spaced as described above to minimize, so far as practical, side lobes directed toward ground undemeath the main lobe. Such a side lobe is indicated in FIG. 3 at 26a and its reflections would coincide with the main lobe 22 and hence interfere with it.

It is generally not feasible to eliminate fully side lobes whose reflections interfere with the main lobe. Accordingly, the main lobe axes of the rhombic antennas 10 and 12 are inclined with respect ground, with the termination of each antenna at a greater elevation than its 5 each inclined tandem-V antenna shown in FIGS. 4 and 5 thus lie in a plane that extends, in the direction of the antennas transverse axis, parallel to ground. The plane of each antennas conductors is inclined by an acute angle with respect to ground along the antennas main lobe axis.

More specifically, the minimum and maximum values of the direct and the reflected waves from a single horizontal tandem-V antenna disposed over horizontal ground occur at the same elevation angles. Thus, as seen in curves 66 and 68 of FIG. 6, which are graphs of signal strength as a function of elevation angle above ground, both the direct and reflected waves of the horizontal antenna (i.e. having both the main lobe and the transverse axes horizontal) have minimum values at 195 and at 34, and maximum values at 27 and at The strengths of the direct and reflected waves thus vary in phase with each other and combine to produce strong peaks at the positions of height-factor maximums and subtract to produce sharp nulls at the positions of height-factor minimums. (The height-factor null positions are marked in FIG. 6 as N-I-IF and the maximums as M-I-IF, with a number prefix.) As a result, the combined (direct plus reflected) radiation shown in curve 70 of FIG. 7 varies widely with elevation angle. This variation also changes substantially with frequency, as indicated above in Table II.

Inclining the main lobe axis of the antenna by an angle of T increases by T the elevation angles at which the direct wave has maximum and minimum values but decreases by T the angles of the reflected wave peaks and nulls. This is shown in FIG. 8 where the curves 72 and 74 correspond to the curves 66 and 68, respectively. More specifically, the curves 72 and 74 are plotted at the same frequency and for the same antenna whose performance is shown in curves 66, 68 and 70, but inclined 8 (i.e. T 8). The overall effect of thus separating by 2T the positions of corresponding direct and reflected wave peaks and nulls is to diminish the height-factor peaks and nulls, so that the combined radiation has less variation in the elevation direction. This is shown by curve 76 in FIG. 9.

With one preferred construction according to the invention, the inclination of the single tandem-V antenna, whose performance is shown in FIGS. 6-9, is selected to make the first null of the reflected wave (curve 68 in FIG. 6) substantially coincide with the first height-factor null. Thus, as shown in curve 74 of FIG. 8, the reflected wave has its first null at 10.5", within 1 of the first height-factor null. As a result, the reflected wave is substantially zero at the first height-factor null and hence does. not noticeably diminish the direct wave. The antennas resultant pattern, curve 76, FIG; 9, has effectively no variation at the position of the first height-factor null.

The elevation characteristics of FIGS. 6-9 illustrate the operation of a rhombic antenna having all four conductors 301 feet long and arranged in two V's, each having half-apex angles m (the angles m are indicated in FIG. 2) of 19. The average elevation of the antenna is 90 feet .and the graphs show its operation at 30 mc. The antenna provides similar operation at frequencies extending to below 5 me.

Referring again to FIG. 6, it will be noted that the nulls and peaks of each of the curves 66 and 68 occur at elevation angle intervals of about 8. This same angle was found desirable for the inclining angle T.

Whereas the antenna whose performance is plotted in FIGS. 6-9 is designed for operation primarily between 5 mc. to 30 mc., it has been found that a tandem- V antenna designed for operation at lower frequencies may advantageously be inclined by one-half the angular interval between successive nulls and peaks of its direct and reflected waves. For example, a rhombic antenna similar to the ones shown in FIGS. 4 and 5 and operating principally between 2 mc. to 12 mc., is advantageously inclined according to the invention by an angle T of slightly less than 5. This is one-half of the 10 elevation angle intervals between peaks and nulls of its direct and reflected waves. By way of illustration, the other dimensions of the 2-12 mc. antenna are m 24; l= 470 ft; and H 123 ft,

where H is the antennas average elevation.

Cancelling side lobes and reflected waves, and adding main lobes, to attain high directive gain would appear to result in narrow-band, frequency sensitive operation, However, the array and other factors combined according to the present invention provide high gain antennas that retain these characteristics over a wide band of frequencies. This is because the factors that are combined in designing antenna systems according to the invention vary with frequency at corresponding rates. I

For example, referring to FIG. 6, the peaks and nulls of the reflected waves and the height-factor nulls and maximums occur at correspondingly larger elevation angles at lower frequencies. That is, the elevation characteristic of the reflected wave and of the height-factor vary similarly with frequency. As a result, the first null of the reflected wave and the first peak of the direct wave occur at the first height-factor null (as shown in FIG. 8) over 10:1 frequency range of the inclined antenna.

It will thus be seen that inclining the main lobe axis of a single long wire antenna in the form of a tandem-V, by the proper angle, greatly improves the elevation characteristic of its radiation pattern. It broadens the elevation plane main lobe pattern and diminishes the effect of an otherwise strong frequency variation on the antenna pattern.

Consider again an array of two tandem V antennas arranged as in FIGS. 4 and 5, to strengthen the main lobe and diminish the side lobe level. The effect of ground reflections on the array is considerably less than on a single tandem-V antenna, due to the smaller amplitude of the side lobes whose reflections interfere with the main lobe.

Moreover, inclining the arrayed antennas in the manner shown in FIG. 5 separates the positions of the array's direct wave peaks and nulls from those reflected from remaining side lobes. The pattern of the resultant inclined array hence has no substantial variation due to ground reflections.

Corresponding to the case of a single tandem-V antenna disposed over ground, the main lobe axes of the arrayed antennas are preferably inclined to make the first height-factor null coincide with a sharp null of the army's free space pattern. The resultant radiation pattern of antennas arrayed according to the invention has, at the most, small side lobes whose ground reflections interfere only slightly with the main lobe. As a result, the arrays main lobe can have a low elevation angle and a wide vertical beam width and still remain relatively free of nulls due to ground reflections. Such a wide frequency-band, low elevation angle and wide vertical beam width system are desirable, for example,

in many long-range communication antennas and in antennas for air to ground or ground to air communication or radar systems.

One antenna array constructed in accordance with the invention has two identical rhombic antennas as shown in FIGS. 4 and 5 with each conductor being 400 feet long, the tilt angle in being approximately 66, and each main lobe axis being inclined 8 with respect to ground. The feed points were about 90 feet above ground and the spacings S and Sy were 90 feet and 18 feet, respectively. The arrays main lobe has vertical coverage from 2 degrees to 30 degrees. It exhibits relatively small change over a :1 frequency range extending from 3 to 30 me. The directive gain of the array is around 20 db over this frequency range and the amplitudes of the largest side lobes are db below the main lobe, with the maximum side lobe occurring at the upper frequency. The input SWR of the antenna is under 2:1 over the frequency range.

The high gain, wide band, double tandem-V antenna array 30 described with reference to FIGS. 4 and 5 requires only approximately 25 percent more land space than a conventional single rhombic antenna. However, the double tandem-V antenna array 82 shown in FIGS. 10 and 11 requires no more land space than a conventional single rhombic antenna and yet provides high gain wide band operation substantially equivalent to the array 30. Moreover, the array 82 requires only two more support towers than a conventional single rhombic.

More specifically, the array 82 comprises two tandem-V antennas 84 and 86 disposed one above the other with common feed apexes 88 and common terminating apexes 90. Conductors 92 and 94 are arranged in a V in the antenna 84 and form its feed apex 88. Conductors 96 and 98 in the antenna 86 are appropriately of the same length as the conductors 92 and 94 and arranged in an identical V that forms the terminating apex 90 of the antenna 86. Similarly, the V- arranged conductors 100 and 102, of equal length and forming the terminating apex 90 of antenna 84, are longer than the conductors 92 and 94 and equal in length to the conducotrs 104 and 106 that form the feed apex for the antenna 86. Thus, the tandem-V antennas 84 and 86 are identical but are disposed with opposite apexes coinciding in space. The spacing 8,, between the transverse axes is measured along the main lobe axes as shown. The spacing S is measured as shown in FIG. 11, between the lines 109 and 111 joining the midpoints of the conductors 94 and 100, and conductors 106 and 98, respectively.

The two tandem-V antennas 84 and 86 forming the array 82 can appropriately be supported from six towers: a lower 108 at the feed apex 88; a tower 110 at the terminating apex 90, and towers 112, 113, 114 and 115 at the sides. Where needed, support cables 116 extend a short distance from each of the towers to the conductors secured thereto. It should be noted that FIGS. 10 and 11 are not to scale. For example, the distancebetween the conductor ends 880 and 88b, at the feed point apex 88, is highly exaggerated, as in the spacing between the conductor ends 90a and 90b. Hence, the distances from the towers 108 and 110 to the conductors attached thereto are actually very short.

In some instances, the antennas 84 and 86 can be constructed with a single tower on each side, one replacing the two towers 112 and 114 and another replacing the towers 113 and 115. The array then has the same number of support towers as a single antenna.

Further, this array can also be constructed with the corresponding apexes vertically spaced apart, along a common vertical line rather than coinciding as shown in FIG. 11.

One array conforming to FIGS. 10 and 11 for optimum operation between 4 MHz and 20 MHZ has conductors 92, 94, 96 and 98 each approximately 127 meters long and conductors 100, 102, 104 and 106, each approximately 176 meters long. The feed apex angle for antenna 86 and the terminating apex angle for antenna 84 are each approximately 14, and the other terminating and feed apex angles are 20. The spacing S is approximately 52 meters and S,, is approximately 2 meters. The first order side lobes of the array are more then 10 db down over the 5:1 frequency range and the lower order side lobes are at least 15 db down from the directive main lobe.

The antenna array of FIG. 12 illustrates the application of the present invention to V antennas, each of which can generally be considered as comprising a tandem-V antenna in which a pair of conductors has zero length. Accordingly, the illustrated array comprises two overlapping V antennas 118 and 120, fed at their apexes 122 and 124 out of phase according to the spacing S between their feed points. Conductors 126 and 128 form the antenna 118 and conductors 130 and 132, generally of the same length as the conductors 126 and 128, form the antenna 120. The illustrated antennas 118 and are above a ground reflector, preferably of substantially unity reflection coefficient, and are inclined with their apexes at a higher elevation than the remote ends 126a,, 128a, a, and 1420 of their conductors. Terminating resistors 134 are connected to ground from the remote ends of the conductors 126-132. The spacings S and S between the V antennas are selected on the bases discussed above with reference to the tandem-V antennas.

In the same manner as discussed above with reference to the graphs of FIGS. 6-9, the main lobe of the resultant pattern that the downwardly inclined V antennas 118 and 120 radiate is relatively free of strong variations with elevation angle when the angle T at which the antennas are inclined is such that peaks and nulls in the reflected wave coincide with nulls and peaks, respectively, in the direct wave. More specifically with an efficient reflector, which can conventionally be achieved by providing a crisscross of conductors on the ground, a downwardly inclined antennas as shown in FIG. 12 has the same radiation pattern as an antenna inclined upwardly at the same angle.

The conductors forming each tandem-V antenna in the above-described arrays embodying the invention may also be disposed in different planes, and the conductors in the V and tandem-V antennas may have unsymmetrical lengths, as in FIG. 2. However, calculations are simplified with the co-planar and symmetrical length constructions illustrated above.

Although the illustrated antennas have only a single conductor in each leg, they may be constructed with a plurality of parallel-connected wires in each leg. For example, each conductor 36, 38, 42, 44 and 48-54 of the array 30, FIGS. 4 and 5, may be constructed with several wires in parallel.

Moreover, the antennas forming the arrays may be constructed without terminating resistors. Reflections from the unterminated ends of the antenna conductors then travel back along the conductors toward the feed point, causing the antenna to radiate energy in the backward direction, opposite to the direction of the main lobe 22 shown in FIG. 3. However, at certain frequencies, the back radiation caused by the reflected energy on the antenna conductors cancels, and the array does not radiate energy in the back direction at these frequencies. The array pattern is then substantially as shown in FIG. 3 and has the high gain as provided by the invention. However, in this instance, the radiation pattern is more frequency sensitive.

Antenna arrays may be constructed according to the invention with more than two V or tandem-V antennas. As an example, such arrays may comprise multiples of two antennas, with each pair being arrayed as described herein and then considered as a single antenna. Two arrays, of two antennas each, can then be arrayed in the manner detailed above for further enhancement of operating characteristics.

More specifically, FIGS. 14 and 15 show a composite array 170 constructed with two sub-arrays 172 and 174, each of which may be identical to the array 82 shown in FIGS. and 11. For clarity, the conductors of the sub-array 174 are shown with dashed lines.

To combine the sub-arrays 172 and 174, the field that each one radiates may be determined as discussed hereinabove. Thereafter, the arrays are considered as single rhombic antennas and arrayed in the same manner as are the rhombic antennas 10 and 12 in the array 30 of FIGS. 4 and 5. Accordingly, the subarrays 172 and 174 of FIGS. 14- and 15 overlap each other and are spaced apart in the horizontal and the vertical directions. Also, they are preferably identically inclined with respect to ground.

Towers 176 and 178 support the apexes of the subarray 172, and towers 180 and 182 support the apexes of the sub-array 174. The sides of one rhombic antenna 172a in the sub-arry 172 are supported with towers 184 and 186, and towers 188 and 190 support the sides of the rhombic antenna 174b in the sub-array 174. The sides of the other antennas 172b and 174a in the subarrays 172 and 174, however, may be supported with a single pair of towers 192 and 194. Thus, the composite array 170 provides further construction economies in that it requires only two towers more than the single array 82 of FIGS. 10 and 11.

When a transmitter, or alternatively a receiver, is connected between the conductors forming the feed apex of a conventional rhombic antenna, the antenna is primarily responsive to energy polarized in the plane of the conductors. This particularly so in the main lobe.

When, on the other hand, the two antenna conductors forming the feed apex are connected together, and energized in parallel by a transmitter connected between them and ground, the energy radiated along the main lobe axis is vertically polarized.

A feed arrangement for energizing long wire antennas for both vertical and horizontal polarization sensitive is shown in FIG. 13 connected with a tandem-V antenna 136. The antenna has electrically symmetrical branches 135 and 137 extending between the feed point and the termination, with at least portions of the branches horizontally spaced apart, i.e. in the direction of a ground relfector. The feed circuit comprises a transformer 138 having a primary winding 140 and a secondary winding 142 provided with a center tap 144.

The secondary winding 142 is connected between the antenna feed terminals 146 and 148. A communication device, illustrated as a transmitter 150, connected across the transformer primary winding then energizes the antenna to radiate energy polarized parallel to the antennas transverse axis 152. A transmitter 154 connected between ground and the center tap 144 energizes the antenna to radiate energy that is vertically polarized.

More specifically, the transformer 138 applies the radio frequency voltage from transmitter across the feed terminals 146 and 148. This voltage between the antennas branches and 137 travels to the termination 156, and, in response, the antenna radiates energy whose electric field is parallel to the traverse axis 152 extending between the branches.

Simultaneously, the transformer winding 142 applies the radio frequency voltage from transmitter 154 to between ground and the feed terminals 146 and 148, with the terminals being excited in phase. This voltage difference between the antenna and ground travels along the two branches to the termination, resulting in energy being radiated with a vertical electric field.

Substantially no voltage from the transmitter 150 appears between the transformer center tap 144 and ground and hence the transmitter 154 is isolcated from the transmitter 150. Similarly, there is no net flux in the primary winding 140 from the transmitter 154 connected to thesecondary winding center tap 144. Accordingly, substantially no voltage from the transmitter 154 appears across the transmitter 150. Grounding one side the transmitter 150, as shown, does not change this isolation between the transmitters.

Alternatively, during reception, the communication devices 150 and 154 are receivers. The antenna 136 delivers the intercepted energy polarized parallel to its transverse axis 152 to the receiver connected to the winding 140. The receiver connected between ground and the center tap 144 receives the intercepted energy that is vertically polarized.

Although two communication devices are shown in FIG. 13, a single transmitter or single receiver may be connected to both the primary winding and between ground and the center tap.

FIGS. 16 17 show a high-low tandem rhomboid array 200 in which two tandem rhomboid sub-arrays 202 and 204 operate over consecutive frequency bands to provide continuous, highly directive operation over an extended frequency range. The upper sub-array 202 operates over the lower portion of the desired frequency range and the lower sub-array 204 operates over the upper portion of the frequency range.

The sub-array 202 is similar to the array 82 of FIGS. 10 and 11 and comprises two tandem-V antennas 206 and 208 that correspond to the antennas 84 and 86 of FIGS. 10 and 11. The antennas 206 and 208 are inclined above the ground reflector by an angle determined in the same manner as discussed above, i.e. to place the first height factor null for the combined antennas at the same elevation angle as the primary null in their free space pattern.

The subarray 204, likewise comprising two tandem- V antennas 210 and 212, is spaced below the sub-array 202.

The feed apex 214 common to the antennas 206 and 208 of the sub-array 202 is vertically in-line with the common feed apex 218 of the antennas 210 and 212 of 

1. An antenna array comprising A. first and second tandem-V antennas
 1. each of which has a feed apex spaced along its main lobe axis from a terminating apex,
 2. each of which has first and second conductors connected to its feed apex and third and fourth conductors connected to its terminating apex with said first and third conductors being connected together and said second and fourth conductors being connected together,
 3. said antennas being disposed a. with the feed apexes thereof along a first common vertical line and the terminating apexes thereof along a second common vertical line, b. with the interconnections in said first antenna of said first and third conductors, and of said second and fourth conductors spaced along said main lobe axis from the corresponding interconnections of said second antenna.
 2. each of which has first and second conductors connected to its feed apex and third and fourth conductors connected to its terminating apex with said first and third conductors being connected together and said second and fourth conductors being connected together,
 2. comprising first and second tandem-V antennas a. uniformly inclined relative to the horizon by a first elevation angle, and b. connected with said first feed port to be energized in parallel therefrom, B. a second antenna sub-array
 2. The antenna array defined in claim 1 in which said conductors of said first and second antennas are so spaced apart in the vertical direction that side lobe peaks and nulls of each antenna coincide with nulls and peaks, respectively, of the array factor for said array.
 2. comprising third and fourth tandem-V antennas a. associated respectively with said first and second tandem-V antennas, b. uniformly inclined realtive to the horizon by said first elevation angle, and c. connected with said second feed port to be energized in parallel therefrom,
 2. has the feed and terminating apexes thereof vertically in line with the feed and terminating apexes respectively of the associated tandem-V antenna of said first sub-array.
 2. coupling energy a. substantially exclusively between said common terminal and said first branch terminal in said first range of frequencies and b. substantially exclusively between said common terminal and said second branch terminal in said second range of frequencies.
 2. comprising at least a second tandem-V antenna formed by a third pair of long wire legs converging together at a feed apex and a fourth pair of long wire legs con-verging together at a terminating apex,
 2. comprising at least a first tandem-V antenna formed by a first pair of long wire legs converging together at a feed apex and a second pair of long wire legs converging together at a terminating apex, B. a second sub-array
 2. comprising at least a second V antenna formed by a second pair of long wire legs converging together at a feed apex,
 2. comprising at least a first V antenna formed by a first pair of long wire legs converging together at a feed apex, B. a second sub-array
 2. the terminating apexes of said first sub-array being intermediate the feed and terminating apexes of said second sub-array, and
 2. having first and second conductors connected to its feed apex and third and fourth conductors connected to its terminating apex with said first and third conductors being connected together and said second and fourth conductors being connected together, D. said two antennas in each sub-array being disposed with corresponding apexes being positioned along common vertical lines, the junctions of said first and third conductors being out of register and the junctions of said second and fourth conductors being out of register, E. said sub-arrays being disposed with
 2. has a first interconnection between one feed-apex-forming leg thereof and one terminating-apex-forming leg thereof and has a second interconnection between the other two legs thereof, B. said first and second sub-arrays are so further arranged that
 2. the other tandem-V antenna in said second sub-array has said two interconnections therein coplanar with said two interconnections of the other tandem-V antenna in said second sub-array.
 3. the junction of said first and third conductors and the junction of said second and fourth conductors of a first antenna in said first sub-array being a. in register, respectively, with the junction of said first and third conductors and with the junctions of said second and fourth conductors of a second antenna in said second sub-array, and b. intermediate the junctions of the other antenna in said first sub-array and the junctions of the other antenna in said second sub-array.
 3. The antenna array defined in claim 1 in which said antennas are inclined with respect to the ground below them with the feed apex of each antenna being at a lower elevation than its terminating apex, the inclination of each antenna being such as to direct substantially a null of a radiated wave of said array in the direction of the first height-factor null of said array.
 3. overlying said first sub-array with the corresponding feed apexes of said sub-arrays being vertically in line with each other, and
 3. overlying said first sub-array with the corresponding feed apexes of said subarrays being vertically in line with each other. C. a common port, and D. means coupling radio frequency signals from said common port substantially only to said feed port of said first sub-array at said first range of frequencies and coupling radio frequency signals from said common port substantially only to said feed port of said second sub-array at said second range of frequencies.
 3. disposed with said third tandem-V antenna overlying said first tandem-V antenna and with said fourth tandem-v antenna overlying said second tandem-V antenna,
 3. said antennas being disposed a. with the feed apexes thereof along a first common vertical line and the terminating apexes thereof along a second common vertical line, b. with the interconnections in said first antenna of said first and third conductors, and of said second and fourth conductors spaced along said main lobe axis from the corresponding interconnections of said second antenna.
 4. arranged and oriented to produce a radiation pattern whose main lobe over said second range of frequencies is substantially spatially coincident with the main lobe of the pattern said first sub-array produces over said first range of frequencies, and C. a feed network
 4. arranged and oriented to produce a radiation pattern whose main lobe over said second range of frequencies is substantially spatially coincident with the main lobe of the pattern said first sub-array produces over said first range of frequencies, C. a common port, and D. means coupling radio frequency signals from said common port substantially only to said feed port of said first sub-array at said first range of frequencies and coupling radio frequency signals from said common port substantially only to said feed port of said second sub-array at said second range of frequencies.
 4. An antenna array comprising A. a first sub-array of two tandem-V antennas, B. a second sub-array of two tandem-V antennas, C. each antenna in each sub-array
 5. The antenna array defined in claim 4 in which said conductors of said antennas of each sub-array are so spaced apart in the vertical direction that side lobe peaks and nulls of each antenna coincide with nulls and peaks, respectively, of the array factor for its sub-array, and in which said sub-arrays are so spaced apart in the vertical direction that side lobe peaks and nulls of each sub-array coincide with nulls and peaks, respectively, of the array factor for said array.
 6. The antenna array defined in claim 4 in which said antennas are inclined with respect to the ground below them with the feed apex of each antenna being at a lower elevation than its terminating apex, the inclination of each antenna being such as to direct substantially a null of reflected radiation of said array in the direction of the first height-factor Null of said array.
 7. A long wire travelling wave antenna array comprising A. a first sub-array
 8. An antenna array according to claim 7 in which said second V antenna has a larger feed apex angle than said first V antenna.
 9. An antenna array according to claim 7 wherein each of said antenna legs comprises at least two substantially coextensive conductors connected in parallel with each other at said feed apex of the V antenna and uniformly vertically spaced apart.
 10. A long wire travelling wave antenna array comprising A. a first sub-array
 11. An antenna array according to claim 10 wherein said terminating apexes of said first and second tandem-V antennas are vertically in line with each other.
 12. An antenna array according to claim 10 wherein said first tandem-V antenna has larger tilt angles than said second tandem-V antenna.
 13. An antenna array according to claim 10 in which A. said first sub-array comprises a first pair of tandem-V antennas arranged to be fed in parallel from said first sub-array feed port and each of which has a feed apex and a terminating apex, B. said second sub-array comprises a second pair of tandem-V antennas arranged to be fed in parallel from said second sub-array feed port and each of which has a feed apex and a terminating apex, and C. each tandem-V antenna of said second sub-array
 14. A long wire travelling wave antenna array comprising A. a first antenna sub-array
 15. An antenna array according to claim 14 in which each tandem-V antenna has a feed apex and a terminating apex and further characterized in that A. each pair of said associated tandem-V antennas is disposed with the feed apexes thereof vertically in line and with the terminating apexes thereof vertically in line, B. said first tandem-V antenna has smaller feed and terminating apex angles and larger tilt angles than said third tandem-V antenna, and C. said second tandem-V antenna has smaller feed and terminating apex angles and larger tilt angles than said fourth tandem-V antenna.
 16. An antenna array according to claim 14 wherein A. each tandem-V antenna
 17. An antenna array according to claim 16 further comprising a plurality of towers supporting said four tandem-V antennas above ground and consisting of A. support towers supporting said tandem-V antennas at said feed and terminating apexes thereof, and B. only four further towers supporting said tandem-V antennas at said interconnections. 